The present invention relates to a process technology for manufacturing a high-density semiconductor integrated circuit element, and in particular, to a wafer-polishing device for flattening the uneven surface of an isolation film or a metallic film deposited on a Si wafer by polishing. In particular, the present invention provides a polishing method having higher stable polishing efficiency than ever by increasing a force for holding abrasive grains on a pad when the wafer is polished and a process for polishing an LSI wafer which can reduce the amount of use of a polishing liquid and a pad.
In a process for manufacturing the high-density semiconductor integrated circuit element, complex bumps and dips are produced on the surface of the LSI wafer by patterning the isolation film or the metallic film. However, when a successive patterning is performed thereon, there may be a case in which since the depth of focus does not have an allowance for the bumps and dips in an exposure process and hence resolution becomes insufficient or a defect is produced on a metallic wiring film at the stepped part of the bumps and dips, a desired high-density semiconductor integrated circuit can not be made. In order to overcome this drawback, a start has been made at using a CMP method in which the LSI wafer is slid with the surface of the LSI wafer pressed onto the turn table on which the pad is placed and in which polishing slurry is poured into a sliding surface to polish and flatten the bumps and dips formed on the LSI wafer.
In the CMP method, a polishing action is performed by the abrasive grains held by the microscopic pits and projections on the pad. Since the amount of polishing per unit time, that is, polishing efficiency becomes higher as the number of abrasive grains held by the pad is larger, the surface of the pad used in the CMP method is shaped into a form for holding the abrasive grains easily. To be more specific, the structure of the pad is made porous and further the surface of the porous pad is dressed with a diamond grinder, whereby the pits and projections on the surface of the pad are controlled to a certain size suitable for holding the abrasive grains.
However, since the microscopic pits and projections on the surface of the pad are abraded as the polishing actions are repeated, the number of abrasive grains held by the pad is decreased and polishing efficiency is reduced. In order to solve this problem, in the conventional CMP method, the pad is dressed every an arbitrary number of wafers. However, there exists a following problem: since the surface of the pad can not be well reproduced after dressing, it is necessary to measure and correct the polishing efficiency, which makes the control of the amount of polishing extremely troublesome. Further, there exists another problem that since the pad is ground to produce a new surface, the consumption of the pad becomes excessive.
On the other hand, in the conventional CMP method, a reduction in the amount of use of slurry is essential. The amount of supply of slurry is about 100 to 200 ml/min, but the number of acting abrasive grains estimated from the polishing efficiency is less than 20% of the number of abrasive grains contained by the slurry. If the number of abrasive grains held by the slurry is increased, the amount of use of slurry is decreased. However, it is considered difficult to increase the number of abrasive grains held by the slurry by holding the abrasive grains with the pits and projections on the conventional pad.
The problem described above is ascribable to holding the abrasive grains with the microscopic pits and projections on the pad. Therefore, in order to solve the problem, it is considered necessary to use another principle such as electrostatic force for holding the abrasive grains.
A method for holding the abrasive grains on the surface of the pad by using the electrostatic force is disclosed in Japanese Unexamined Patent No. 62-8566. The object of the invention is to eliminate low polishing efficiency in a non-contact polishing method. In the invention, an extremely light load of about 10 to 40 gf/cm2 is applied to the surface of a work and, in order to put the abrasive grains into soft contact with the work, a soft pad such as fine woolly structure or foamed polyurethane having low hardness is used as a body for holding the abrasive grains. Therefore, there exist a problem that although the roughness of the surface of the work is good, this constitution as it is, is not sufficient in the ability of flattening the bumps and dips on the work which is required in the CMP.
It is the object of the present invention to provide means for improving and stabilizing polishing efficiency in the CMP of the LSI wafer and for reducing the amount of use of the polishing liquid and the pad by increasing the force for holding the abrasive grains on the pad.
An electric field is applied to the abrasive grains on the pad to attract the abrasive grains into a diffusion layer in a polishing liquid solvent near the surface of the pad, thereby holding the abrasive grains in the diffusion layer. A resin plate made of non-foamed material and having flatness and rigidity is used as the pad.